A popular particular food product are French fried potatoes which, in considerable amounts, arc served in portions in restaurants, grill bars, cafeterias or in the street from hot-dog stands. French fried potatoes are served either alone as a meal by themselves or in connection with other courses. In any case, there will be a demand for French fried potatoes being freshly heated and crispy immediately after the order has been placed. Since French fried potatoes are unsuitable for long term keeping in this condition, the preparation must necessarily take place by means of a process which quickly and easily can transform the raw and possibly pre-processed material into the ready product.
This demand is to the utmost fulfilled by deep-fat frying, where a basket containing a portion of potato strips is lowered into a pool of melted lard or cooking oil. The lard or the oil is quickly absorbed by the potato strips which thereby are heated and given a crispy and crunchy consistency with an almost brown color, mainly deriving from a caramelizing of the sugar content of the potato pieces.
When the potato pieces are treated in this way, they will as French fried potatoes have a fatty or oily content of 30%. Considering the very big amounts of French fried potatoes which over the years are consumed especially in the industrialized countries, this otherwise so popular food product can be a serious threat to national health. Frequently consuming too much fat could in the long run be deposited as fatness and cause various diseases.
In order to eliminate these problems, various apparatuses have been invented concerning treatment of pre-processed potatoes containing a relatively low content of fat. With these apparatuses, it is possible to make crispy and tasty French fried potatoes with a moderate fatty content of approximately 6%.
In this way, the problem of the high fatty contents in deep-fried potatoes has been relieved, but in deep-frying as well as in more simple apparatuses, it still is a big problem that the process sends smoke and smell out into the surroundings to the inconvenience of the serving staff and the customers present in the room. Some apparatuses have therefore been supplied with filters for cleaning the air before it reaches the room. Neither of these apparatuses have fully lived up to the demands made on them.
The apparatus as invented is suitable for treatment of pre-fried potato pieces with a fatty content of, for example, approximately 6%. The potato pieces also contain water which partly has to be removed in order to obtain the crisp and crunchy consistence of the potato pieces which is characteristic of French fried potatoes. This means that a successive renewal of the air in the treatment chamber has to take place as the process otherwise will be hampered or stopped, when the air in the chamber has been saturated with vapor.
The air renewal takes place when the ventilator sucks air out of the treatment chamber while fresh air is pressed into it via an opening for influx of air in the wall of the chamber. In this way, an air flow is produced which is to be thrown off into the open. Out of consideration for the surrounding environment, it is, prior to that, necessary to let the air flow pass the filter device to remove the air contents of vapor, fat, smell and other impurities.
The temperature of the air in the treatment chamber can reach about 250.degree. C. at least in the final step of the process. If air with such a high temperature is sent through the filter device, this might be damaged and might work with reduced effectiveness so that the air will not be cleaned satisfactorily. To relieve this problem, the air flow could be increased in excess of the optimum progress. However, that would imply extra running expenses for heating the additional air volume and furthermore both ventilator, filter and other construction details of the apparatus would have to be laid out with correspondingly large dimensions, whereby the apparatus would be clumsy and bulky, and it would be exorbitantly costly to produce.
By using the air connection between the treatment chamber and the filter device as convector, the air can now be cooled down to a temperature most suitable for the filter device. Normally, the various components will be built in a cabinet. In the wall of the cabinet, it would be a good idea to construct holes as well above as under the area where the convector is placed. The buoyancy in the heated air surrounding the convector will then force a secondary air flow past the convector, whereby the primary air flow in the convector is cooled down. In the same way, a secondary air flow can be sent past areas of the cabinet wall which are close to the very hot treatment chamber. Thereby, these areas are cooled and will therefore not be uncomfortably hot for the persons who are to operate the apparatus.
When the components of the apparatus are built in a cabinet, it will be appropriate to construct a lead-in opening with a corresponding door in both cabinet and treatment chamber. By interconnecting the two doors with a suitable rod system, they can be made to open and close simultaneously. The serving staff will therefore only have to open the outer door of the cabinet to get immediate access to the treatment chamber when this has to be filled with a new portion of potato pieces. In this connection, the two doors can be hinged in such a way that they, in open position, together form a lock between the treatment chamber and the cabinet, through which the product easily and safely can be poured into the treatment chamber.
The convector can be constructed in many different ways within the scope of the invention. Thus, it can be constructed as a channel with ribs which give the convector a large surface for effectively transmitting the heat contents of the primary air flow to the secondary air which flows past the convector. In an especially advantageous embodiment, the convector can consist of a number of heat-conducting pipes which are placed at intervals side by side in such a way that the secondary air flow can pass between the pipes which for example can be made of copper or another heat-conducting material.
For heating the potato pieces, radiant heat from, for example, quartz lamps can advantageously be used. This is a very intensive form of energy providing a quick and precise heat treatment of the potato pieces with minimum energy loss to the surroundings. The heat-ray element will then naturally be placed inside the treatment chamber which may be constructed in different ways. For example, the chamber may be a rotating cylinder in which the potatoes during the rotation are tumbling between each other and are therefore uniformly irradiated on all sides. In a preferred embodiment, the treatment chamber is stationary, and the potato pieces will be rotated by rotating a driving wheel with carriers.
The stationary construction of the treatment chamber means that the inlets and outlets and the closing mechanism of these can be constructed in a simple and reliable mainer. The out-let can thus conveniently be constructed permanently in the bottom area of the treatment chamber. In this way, the ready French fried potatoes will automatically fall out under the influence of the gravitational pull when a slide gate in front of the emptying opening is pulled away. By letting the driving wheel continue to rotate during this, a complete emptying of the treatment chamber takes place.
The French fried potatoes fall through a shaft which is constructed in the cabinet and has an opening at the bottom, through which a sleeve for collecting the French fried potatoes can be inserted. The fresh French fried potatoes will immediately after the heat treatment continue to smell, however, the smell will be sucked into the treatment chamber via its air in-let, as the ventilator under this will continue to be operating.
An apparatus of the above named type is known from patent application WO 95/13734.
In this apparatus which, as mentioned, subject the potato pieces to intense radiant heat, the quartz lamps for heating the potatoes will necessarily have to operate with a rather high surface temperature, which for example can exceed 800.degree. C. At such high temperatures, there is a risk that substances in the vapors, which the potato pieces give off when they are irradiated, can disintegrate near or on the quartz lamps and form malodorous and unhealthy compounds of, for example, aldehydes which can be both saturated and with a double bond in 2-position.
As example of such aldehydes can be mentioned acrolein or 2-propenal which has a pungent and unpleasant smell, and higher unsaturated aldehydes which smell like acrolein though with a slightly less strong and pungent smell.